On board diagnostic (OBD) devices in vehicles are known from the related art. With the aid of OBD, components of an internal combustion engine in a vehicle may, in particular, be monitored which have an effect on a property of an exhaust gas of the internal combustion engine. Errors occurring in relation to a property of the exhaust gas are detected by the OBD and displayed to the driver of the motor vehicle via an indicator light, for example, as well as permanently stored in an associated control unit. OBD was first introduced in 1988 by the California Air Resources Board (CARB) against the background that the exhaust gas regulations should not only be complied with at the registration of the motor vehicle, but should also be ensured during its lifetime. Within the scope of the further development of the second generation of the electronic systems for self-monitoring (CARB-OBD II), which is presently in use, a diagnosis of cylinder-selective mixture errors, which are relevant to the exhaust gas, is required, among other things. These types of mixture errors are essentially based on the fact that in an arrangement of at least two cylinders in a system, which includes an internal combustion engine, not necessarily every cylinder is set to the optimum ratio of combustion air and fuel (lambda=1) in the case of which what may be a complete consumption of oxygen from the combustion air takes place in the fuel. This condition of cylinders in the internal combustion engine which occurs in practice is usually referred to as “imbalance.”
The determination of the imbalance of at least one cylinder generally takes place with the aid of a sensor device for detecting at least one property of an exhaust gas of the internal combustion engine. Sensor devices of this type, which in particular include lambda sensors, are known from the related art and are described, for example, in Konrad Reif, publisher, Sensoren im Kraftfahrzeug [Sensors in a Motor Vehicle], Springer-Vieweg 2. edition, 2012, pages 160-165. In this case, so-called “two-point lambda sensors” compare the residual oxygen content in the exhaust gas to the oxygen content of a reference gas atmosphere, which may be present in the interior of the sensor device as recirculating air and show whether a rich mixture (Lambda<1) or a lean mixture (Lambda>1) is present in the exhaust gas. Due to its configuration, an abrupt change, which only allows the composition of the mixture to be adjusted to lambda =1, however, occurs at lambda =1 in the characteristics curve of the two-point lambda sensor. In contrast thereto, the oxygen concentration in the exhaust gas may be determined over a wide range with the aid of a “broadband lambda sensor,” wherefrom the air/fuel ratio in the combustion chamber of the internal combustion engine may be inferred. The broadband lambda sensor may therefore not only determine the oxygen concentration in the exhaust gas of the internal combustion engine in the stoichiometric point at lambda=1, but also in the lean mixture (Lambda>1) as well as in the rich mixture (Lambda<1). In addition to the speed-based methods, methods are also already known for determining the imbalance of a cylinder which are based on detecting the progression of the lambda value within a combustion cycle of the internal combustion engine. The combustion cycle of the internal combustion engine, which is defined as that period of time during which each of the at least two cylinders has been ignited once, is used to determine from a difference of a maximum lambda value and a minimum lambda value a so-called “peak-to-peak” value which is correlated with the fact of how a cylinder deviates, i.e., is trimmed, from the rest of the cylinders present in the internal combustion engine.
This value may be used to determine with the aid of an evaluation algorithm an evaluating signal which may also be referred to as an “air/fuel imbalance monitoring” (AFIM) signal. With regard to the real imbalance of the cylinders in the internal combustion engine, in practice, the evaluating signal is, however, subject to a dispersion which may result in potential erroneous detections. Keeping the influence variables in the system, which includes the internal combustion engine, which may be constant, generally requires a lot of effort, however. It would therefore be desirable to provide a method for determining an imbalance of at least one cylinder in an arrangement of at least two cylinders in a system which includes an internal combustion engine, this method may largely delimit the range of potential erroneous detections due to the dispersion of the real imbalance of the cylinders.